Chapter 12: Heart and Cardiovascular System

Heart

pumps blood through over 60,000 miles of blood vessels, contains striated muscles and cardiocytes

Cardiocytes

cardiac muscle cells

Cardiocyte Structure

smal cells and nucleus, short wide T tubules (no triads), aerobic metabolism, intercalated discs

Intercalated Discs

• specialized contact points that join cardiocyte membranes via gap junctions

• desmosomes maintain structure

• enhance molecular and electrical connections, and conduct action potentials

• link cardiocytes mechanically, chemically, and electrically

Automaticity

contraction without neural stimulation

Functional Characteristics of Heart

• automaticity

• controlled by pacemaker cells

• larger mitochondria generate ATP aerobically

• long refractory period

Functional Characteristics of Heart: Contraction

• neural input controls contraction tension

• prolonged contraction time is 10x longer than skeletal muscle

• sustained contraction due to slow calcium delivery

• no wave summation or tetanic conctractions

Cardiovascular System

pumps blood through pulmonary and systemic circuits, blood flows alternates between them

Pulmonary Circuit

carries blood to and from the lungs

Systemic Circuit

carries blood to and from the body

Cardiac Anatomy

4 chambers: left and right atrium, left and right ventricle

Heart Chambers

contract in unison to deliver equal volumes of blood through the pulmonary and systemic circuits

Heart Location: Mediastinum

region between pleural cavities, contains heart, great vessels, thymus, esophagus, trachea

Pericardium

sac-like network of collagen fibers (serous membrane), double lining of pericardial cavity

Visceral Pericardium

inner layer of pericardium

Parietal Pericardium

outer layer of pericardium, inner layer of pericardial sac

Pericardial Cavity

lies between parietal and visceral layers, contains pericardial fluid (15 - 50 mL)

Pericardial Sac

composed of dense, fibrous tissue that surrounds and stabilizes heart

Pericarditis

inflammation of the pericardium

Cardiac Tamponade

excess pericardial fluid, restricts movement

Auricle

an expandable extension of the atria

Coronary Sulcus

groove at the border between atria and ventricles

Anterior and Posterior Interventricular Sulci

grooves at the border between ventricles

Sulci

contain fat and coronary vessels

Coronary Sinus

collects blood from cardiac veins, delivers it to right atrium

Superior Vena Cava

returns blood from the head, neck, upper limbs, and chest

Inferior Vena Cava

returns blood from the trunk, viscera, and lower limbs

Layers of Heart Wall

epicardium, myocardium, endocardium

Epicardium

visceral pericardium (covers heart)

Myocardium

concentric layers of cardiac muscle, consists of atrial and ventricular myocardium

Endocardium

inner epithelial layer

Atrial Myocardium

wraps around great vessels

Ventricular Myocardium

superficial (wraps ventricles), deep (spiral around and in between ventricles)

Internal Features of Heart

interatrial septu,, interventricular septum, atrioventricular valves

Interatrial Septum

separates the atria

Interventricular Septum

separates ventricles

Atrioventricular Valves

folds of fibrous tissue that connect atria to ventricles and permit blood flow in only one direction

Foramen Ovale

opening present before birth that connects the atria, seals off at birth (fossa ovalis)

Pectinate Muscles

prominent muscle ridges found in the anterior atrial wall, receives blood from right atrium

Right Atrioventricular (AV) Value

tricuspid valve, broad opening with 3 fibrous flaps or cusps that are attached to chordae tendineae

Papillary Muscles

connect flaps to ventricular wall through chordae tendineae

Chordae Tendineae

tension produced in these prevent valves from opening back to atria during ventricular contraction, prevents blood backflow

Trabeculae Carneae

muscular ridges in ventricular wall

Moderator Band

muscular band that connects the interventricular septum to anterior papillary muscles (part of the conduction system)

Conus Arteriosus

conical pouch ending at the pulmonary valve

Pulmonary Semilunar Valve (3 Cusps)

regulates blood flow into the pulmonary trunk from the right ventricle to the lungs

Left and Right Pulmonary Arteries

receive blood from the pulmonary trunk and then continue to branch toward capillary beds of lungs, blood flows from respiratory capillaries into 4 pulmonary veins

Left and Right Pulmonary Veins

deliver oxygenated blood to the left atrium

Bicupsid Valve (Mitral Valve)

• 2 fibrous cusps allow blood flow into left ventricle

• holds the same volume as right ventricle but has very thick walls making the left ventricle much larger

• has prominent trabeculae carnae but no moderator bond

Aortic Semilunar Valve (3 Cusps)

allows blood to leaves the ventricle to the ascending aorta, through the aortic arch and into the descending aorta

Ligamentum Ateriosum

a fibrous band connecting the aortic arch and pulmonary trunk

Atria Features

similar in size and function

Right Ventricle Features

pouch shaped, thin wall, required to produce less pressure

Left Ventricle Features

round, thick walls, requires 4-6x pressure of right to push blood through systemic circulation

Ubiquitous Connective Tissue

adjacent cells are connected by struts, provides physical support and elasticity, helps to distribute contraction forces, adds strength and prevents overexpansion

Struts

fibrous cross links

Cardiac Skeleton

4 dense bands of elastic tissue that stabilize the position of valves, electrically insulates ventricular muscle cells

Regurgitation of Blood into Atria

occurs from damaged cusp

Valvular Heart Disease (VHD)

a deterioration of valve function often due to inflammation of the heart, microbial (bacteria or virus) or congenital

Carditis

heart inflammation

Rheumatic Fever

inflamatory response to streptococcal bacterial infection, initial diagnosis by auscultation

Auscultation

use of a stethoscope to listen to heart sounds, sound from turbulence in blood flow caused by valve closure

Lubb: 1st Sound

atrioventricular (AV) valves closing

Dubb: 2nd Sound

semilunar valves closing

Coronary Circulation

heart pumps continuously but needs a reliable supply of oxygen and nutrients, myocardium has dedicated blood supply

Left and Right Coronary Arteries

vessels with the highest blood pressure, originate at the aortic sinuses at the base of ascending aorta

Elastic Rebound

occurs when blood entering the aorta stretches the most elastic artery in the body

Coronary Circulation

the ventricle relaxes, recoiling the aorta and pushes blood through the system circuit

Left Coronary Artery

• involved in myocardial infarction, often called widow-maker

• supplies blood to the left atrium, left ventricle, and the interventricular septum

• contains arterial anastomoses, circumflex artery, anterior intreventricular artery

Right Coronary Artery

• runs along the coronary sulcus, supplies blood to right atrium, portions of both ventricles, and portions of conduction system

• branches to marginal arteries

• continues to posterior interventricular artery

Marginal Arteries

run over the surface of ventricles

Posterior Interventricular Artery

supplies septum and portions of ventricles

Arterial Anastomoses

interconnect posterior and anterior interventricular arteries and help to stabilize blood supply to cardiac muscle

Circumflex Artery

curves around coronary sulcus and fuses with branches of right coronary artery

Anterior Interventricular Artery

curves around pulmonary trunk and runs along surface of anterior interventricular sulcus

Great Cardiac Vein Location

runs along anterior surface of ventricles along interventricular sulcus and ascends to atria along the coronary sulcus

Great Cardiac Vein Function

drains blood from region supplied by anterior interventricular artery, empties into coronary sinus, all other veins empty into great cardiac vein

Small Cardiac Vein

drains posterior surface of right atrium and ventricle

Anterior Cardiac Vein

drains anterior surface of right ventricles and empties directly into right atrium

Posterior Cardiac Vein

drains circumflex artery

Middle Cardiac Vein

drains posterior interventricular artery

Bifurcations in Coronary Vessels

points where a coronary artery divides into two branches e.g left main coronary artery (LAD + circumflex artery)

Bifurcations Significance

natural sites of turbulent blood flow, increasing risk of plaque formation and blockages

Bifurcations Clinical Relevance

sites prone to atherosclerosis, can lead to myocardial infarction, important consideration in angioplasty and stent placement

Coronary Artery Disease (CAD)

partial or complete blockage of coronary circulation, blockage reduces blood flow and decreases cardiac performance

Coronary Ischemia

a condition in which cardiac muscles are not receiving adequate oxygen due to decrease in blood flow

Coronary Artery Disease Causes

caused by fatty deposit (atherosclerotic plaque) in vessel wall

Thrombosis

plaque or associated clot

Coronary Artery Disease: What Happens

• thrombosis narrows vessel and reduces blood flow

• spasms in vessel smooth muscle can further reduce blood flow

• exertion or stress can produce sensation of pressure, chest constriction or pain

• symptoms can radiate from sternal area to arms, back and neck

Angina Pectoris

development of temporary ischemia when workload increases

Myocardial Infarction

• heart attack

• caused by blockage of coronary circulation

• results in cardiac cell death due to lack of oxygen

• severity depends on site and extent of blockage

• usually accompanied by intense pain even at rest

Myocardial Infarction Blockage

blockage in small arterial branches or near coronary arteries

Silent Heart Attack

no symptoms, very dangerous, often goes undiagnosed

Diagnosis of Myocardial Infarction

ECG, blood test, 25% myocardial infarction patients die before getting medical help

Infarct

nonfunctional area of heart

Diagnosis of Myocardial Infarction: Blood Test

• damaged cardiac cells release cardiac enzymes

• blood is screened from presence of cardiac troponin T and I, and cardiac creatine phosphokinase

Myocardial Infarction Treatment Options: Drugs

anticoagulants, vasodilators, calcium channel blockers

Myocardial Infarction Treatment Options: Noninvasive Surgery

atherectomy, balloon angioplasty, stent

Myocardial Infarction Treatment Options: Coronary Artery Bypass Graft

detour around obstruction

Heartbeat

single cardiac contraction